Biomechanical Assessment of Pin-Site Fractures in Intra- versus Extra-Incisional Pinning Technique for Robotic Total Knee Arthroplasty: A Cadaver Study.

Abstract

Robotic-assisted total knee arthroplasty (rTKA) offers enhanced precision, but introduces new challenges, including pin-site fracture risk from tracker fixation, with incidence rates of 0.06 to 4.8%. This study aimed to evaluate the effects of intra- versus extra-incisional pin placement on torsional rigidity to fracture failure in cadaver specimens. There were 20 matched cadaver femora and tibiae that were randomized to undergo either intra-incisional/metaphyseal or extra-incisional/diaphyseal pinning. Specimens were cemented into jigs and subjected to torsional load-to-failure in two stages, first at 100 Nm, then at 300 Nm, with two separate machines, with continuous monitoring of torque, rotation, and time. Fracture documentation and trendline analysis were performed to calculate torsional rigidity and coefficient of determination (R²). Fracture characteristics, including pin-site involvement, and fracture patterns were also recorded. Mean torsional rigidity was significantly higher for intra-incisional femora at both 100 Nm (14.03 versus 10.91 Nm/degree, P = 0.048) and 300 Nm (14.46 versus 10.91 Nm/degree, P = 0.048). There were 80% of extra-incisional femora that fractured when subjected to 100 Nm of torsion, compared to 20% of intra-incisional femora (P = 0.058). The mean torsional rigidity was 8.24 Nm/degree for intra-incisional compared to 6.35 Nm/degree for extra-incisional pinning for tibiae (P = 0.2), although this did not reach statistical significance. There were 80% of extra-incisional tibiae that fractured when subjected to 100 Nm of torsion, compared to 40% of intra-incisional tibiae. Overall, 80% of extra-incisional specimens fractured, compared to a significantly lower 30% of intra-incisional specimens (P = 0.025). There were half of the extra-incisional specimens had fractures that involved the pin site(s), compared to none in intra-incisional specimens. Intra-incisional pin placement confers biomechanical advantages by having significantly higher torsional rigidity and reduced fracture risk, particularly of pin-site failures, in both femora and tibiae compared to extra-incisional pin placements. Patients who are encouraged to ambulate immediately after rTKA operations may have a better safety profile by using intra-incisional pinning techniques.